Trans Maldivian DHC6 at Male on Oct 5th 2020, sudden roll to the right and left during water landing
Last Update: September 23, 2021 / 19:32:21 GMT/Zulu time
The aircraft taxied to the mooring with the right hand engine only, a dinghy assisted pushing the left hand float. Passengers and crew disembarked normally. The aircraft was subsequently moved to a maintenance dock for assessment of the damage.
On Nov 5th 2020 Madives Accident Investigation Coordination Committee (AICC) released their preliminary report describing the damage:
Survey of the aircraft by accident investigators identified the extent of the damages sustained to the airframe, wing, engines and propellers. The damages identified include but not limited to:
1. Right Hand Wing:
a. Various damages in the area between ribs 25 to 28
b. The leading-edge bottom skin towards the wingtip buckled upwards
c. Wing tip severely crushed and material missing
d. Wing fin dislocated with the leading edge shifted outboard
e. The inboard trailing flap skin buckled upward
2. Left Hand Wing:
a. Leading edge bottom skin buckled upwards
3. Left Hand Propeller:
a. LH propeller blades (all three of them) bent aft
b. LH propeller assembly dislocated
No apparent damage observed.
The captain (42, ATPL, 12,329 hours total, 3,417 hours on type) was pilot flying, the first officer (24, CPL, 2,808 hours total, 2,543 hours on type) was pilot monitoring.
On Sep 23rd 2021 the AICC released their final report concluding the probable causes were:
The causes / contributing factors of this accident were:
- Loss of control on landing;
- Varying crosswind conditions during landing;
- Lack of practice or experience (change of motor skills) of the PIC for landing floatplanes.
The AICC analysed:
The DHC-6 aircraft, had no known system malfunctions, maintenance overruns or open deferred defects that would have contributed to the accident, and therefore those are ruled out as contributing factors. Hence, the analysis is focused on flight operations; handling of the aircraft during approach and landing, crew training and weather conditions that existed.
The aircraft, operating under VFR had three crew (two pilots and one cabin crew) onboard and a total take off mass of 10,588 lbs. with its CG located between Forward (25%) and Aft (32%) MAC and sufficient fuel (820 lbs: Mass & Balance Report) to complete the flight.
Both cockpit crew were qualified, proficiency-checked and experienced on type. PIC held a valid ATPL with a total of over 12,000 flying hours, including 3302 hours on DHC-6 float planes (between 2008-2011) and 8600 hours on Dash-8 aircraft (DHC-8) on land (between 2011 to 2019). Beginning January 2020, the PIC started flying the DHC-6 float aircraft, gaining 60.38 hours as PIC under supervision, and another 51.32 hours as PIC.
The FO held a CPL with a total of 2,808 flying hours which includes 2543 hours on type. Both held valid medicals and proficiency checks too.
The FO had only been flying the DHC-6 floatplanes since completion of the ab-initio training, however.
The destination - Velana International Airport, abbreviated as VIA (04° 11’ 30” N, 073° 31’ 45” E) is the main airport of entry into and departure from the Maldives. The lagoon located on the eastern side of VIA is used as a waterdrome dedicated for operating floatplanes.
Floatplanes take-off and land along specific paths that are partially delineated and referred to as, ‘North Left’, ‘North Right’ and ‘South Left’ so that repeatability and predictability can be anticipated by all operators and ATC as well. However, under challenging weather conditions, takeoff and landing operations are permitted by ATC in north-east/south-west and east/west directions on a case by case basis.
When the crew briefed the approach, they were aware that VIA was experiencing light rain and winds from the west at about 290 / 20 knots, a left crosswind for the aircraft approaching from the south to land on the area referred to as ‘North Right’ (cleared for landing by ATC). The prevailing weather condition was assumed unpredictable. The Maximum Demonstrated Cross Wind for DHC-6 Twin Otter aircraft on Floats is 17 knots.
Just after touch down, the aircraft rapidly banked/rolled to the right with the right float and wing dipping into water with the left wing rising high in the air, and swerved to the right until the aircraft was facing south (opposite direction to landing); then the left wing dropped to the water and the aircraft settled down afloat.
The PIC who was the PF had been operating DHC-8 (land planes) for a considerably long period prior to reconverting to DHC-6 (floatplane) beginning January 2020. It took 60.38 hours for him to be finally released for line flying. This is more than the operator’s standard 25 hours required for a PIC to be released for line flying.
Following release to the Line Flying, like many others, the PIC did not have the opportunity to undertake flying primarily due to lack of air transportation activities resulting from the lockdown imposed in the country to control spread of Covid-19 virus. He had only 37.5 hours of flying during the last 90 day period prior to the accident flight.
Past incidents/accidents reveal that pilots who transit from wheeled airplanes to float airplanes have often had difficulty in mastering the motor skills necessary to maintain the proper attitude for water landing within the time period specified in the Operations Manual.
In this case the extra time taken by the PIC to be released could have contributed to: the lull in flying activity that prevailed during the Covid-19 pandemic and the longer time the PIC took to master the landing attitude of the floatplanes, which contrastingly differ to that required to land wheeled airplanes on land.
Aircraft operating crew and the airport Fire and Rescue team acted swiftly, and thereafter assisted the aircraft to the dock where the occupants were disembarked safely. There were no fatalities but some had minor injuries which were later examined and treated at the hospital.
This article is published under license from Avherald.com. © of text by Avherald.com.
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